ValueMapper: Fix unused var warning. NFC
ValueMapper: Fix unused var warning. NFC

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@266529 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit db4fbb66b3a86d061feb3f00e442803b3daf1e35)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm